现行黄河口区的水沙动力与汊道演变

Water and Sediment Dynamics of the Active Yellow River Mouth and Its Evolution of Distributary Channels

近年来黄河入海水沙量持续减少,河口水沙动力和地貌演变出现了新的情势。基于黄河口区实测水文泥沙和利津站水沙数据等,阐述目前黄河口的水沙动力与汊道演变。研究发现,现行黄河口区潮汐存在“潮位一升一降,潮流二次往复,流速四峰四谷”的特征,形成了涨潮北流、涨潮南流、落潮北流和落潮南流4种流动形式,以及近岸与远岸对峙的余流场;河口径流量减少,潮流界和潮区界有所上溯;口门东、北两汊涨落时刻不同步,形成了短时汊道环流。剪切应力计算结果显示,口外悬沙含沙量主要取决于床面的泥沙动态,悬沙含沙量主要受泥沙的沉降和再悬浮控制。口门进出潮水量计算结果显示,口门进潮量北汊大于东汊,而入海水量北汊小于东汊,表明目前北汊趋于衰退,而东汊将逐渐成为径流入海的主汊。

The water discharge and sediment load of the Yellow River into the sea have been decreasing in the last decades,and accordingly the water and sediment dynamics and morphological evolution in the river mouth have presented a new regime.Based on the measured hydrol⁃ogy in the river mouth and the collected water and sediment discharges at Lijin Hydrological Station,this paper examined the water and sedi⁃ment dynamics and the distributary channel evolution in the mouth.The results show that a tide cycle has the characteristics that the tide level rises and falls one time,the tidal current is repeated twice,and the current velocities are four peaks and four valleys.Four kinds of currents,i.e.northward flow of flood tide,southward flow of flood tide,northward flow of ebb and southward flow of ebb,and residual current confront⁃ing between the nearshore and offshore has been formed.The tidal current and tidal limits have moved upstream due to decreased runoff.Be⁃cause the times of flood and ebb at the east and north branches are not synchronous,short⁃time bifurcation channel circulation forms in the river mouth.The calculation of bottom shear stress shows that the suspended sediment concentration(SSC)outside the mouth mainly depends on the sediment dynamics of the seabed,the SSC is primarily controlled by sediment resuspension.The calculation of in and out water vol⁃umes shows that the tidal prism is larger in north branch than that of in east branch,while the water volume into the sea is smaller in north branch than that of in east branch.The results show that the north branch tends to decline,while the east inlet will become the main inlet of runoff into the sea.